Apparatus for heat treating workpieces

ABSTRACT

The loading, preheat, high heat and cooling vessels of a heat treating apparatus are connected end-to-end by unitized door modules each containing within itself a sealing door for isolating the atmosphere in each vessel from that in the other vessels and also containing one or more heat shielding doors for blocking the escape of heat from the heating vessels. Door modules also are connected to the entrance end of the loading vessel and to the exit end of the cooling vessel and contain sealing doors for sealing off such vessels from the outside atmosphere.

United States Patent [72] Inventor June R. Bornor [56] References Cited I Rockford, UNITED STATES PATENTS g 95:;- M 53 802,517 /1905 Kugel 263/37 Patented June 8,197! 3, 90,547 ll/l968 Blelefeldt ll0/l 73 X [73] Assignee Alco Standard Corporation P im y X m 0hn J Camby Valley Forge, Pa. Att0rneyWolfe, Hubbard, Leydig, Voit and Osann ABSTRACT: The loading, preheat, high heat and cooling ves- [54] TREATING sels of a heat treating apparatus are connected end-to-end by 7 CI 8 D unitized door modules each containing within itself a sealing 1 rawmg door for isolating the atmosphere in each vessel from that in [52] U.S. Cl 263/36, the other vessels and also containing one or more heat shield- 1 10/173 ing doors for blocking the escape of heat from the heating ves- [51] Int. Cl ..F27b 19/04, sels. Door modules also are connected to the entrance end of F23m 7/00 the loading vessel and to the exit end of the cooling vessel and Field of Search 263/36, 37, contain sealing doors for sealing off such vessels from the out- 38,39; /173 side atmosphere.

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PATENTEU JUN 8 l97l SHEET 1 [IF 3 APPARATUS FOR HEAT TREATING WORKPIECES BACKGROUND OF THE INVENTION This invention relates to apparatus for heat treating workpieces and, more particularly, to apparatus of the type which includes a plurality of interconnected vessels having work chambers through which the workpieces are sequentially transferred during various stages of the heat treating operation. The work chambers, at least one of which is a heating chamber, are disposed end-to-end and are adapted to be sealed by doors that isolate the atmosphere in each chamber from that in the other chambers and also block the escape of heat from the heating chambers. The doors are located at the ends of the various vessels and are adapted to be moved to open positions by actuating mechanisms to permit passage of the workpieces into and out ofthe chambers.

SUMMARY OF THE INVENTION The primary aim of the present invention is to provide a new and improved heat treating apparatus of the above character in which the various vessels may be arranged end-to-end, interconnected and interchanged in a simpler, easier and more versatile manner than has been possible heretofore. In large, the foregoing ends are achieved through the provision of unique door modules adapted to be connected to and between the ends of the vessels and containing within themselves the requisite doors for blocking and sealing the work chambers, along with actuating mechanisms for opening and closing the doors, so that the different vessels may be arranged in any desired fashion merely by selecting appropriate door modules and utilizing the latter to interconnect the vessels.

The invention also resides in the novel construction of the door modules as self-contained units, in the ease of adaptability of the modules for use in conjunction with different types of vessels, and in the unique arrangement of the doors of the modules to enable the use of a single module for blocking the escape of heat from two adjacent heating chambers while establishing a gastight seal between the chambers.

These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation ofa new and improved heat treating apparatus embodying the novel features of the present invention.

FIG. 2 is a side elevation of one of the door modules adapted to be connected to one end ofone of the vessels.

FIG. 3 is a side elevation of one ofthe vessels.

FIG. 4 is a side elevation of a door module adapted to be connected between the opposing ends of adjacent vessels.

FIG. 5 is an enlarged fragmentary cross section taken vertically through the apparatus shown in FIG. 1.

FIG. 6 is a cross section taken substantially along the line 6-6 of FIG. 5.

FIG. 7 is a cross section taken substantially along the line 7-7 of FIG. 6.

FIG. 8 is a fragmentary cross section taken substantially along the line 8-8 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings for purposes of illustration, the invention is embodied in a heat treating apparatus in which metal workpieces I (FIG. are heated to high temperatures in either a vacuum or a controlled nonoxidizing atmosphere and then are cooled by a quenching gas. Heating of the workpieces within a vacuum or controlled atmosphere prevents oxides from forming on the heated surfaces, while quenching with a cooling gas improves the physical properties of the metal of the workpieces.

Herein, the workpieces I0 are carried on cars ll (FIG. 5) and initially are shifted from a transfer cart 13 (FIG. 1) into a loading chamber 14 which then is evacuated or purged with a nonoxidizing gas prior to transfer of the workpieces to a preheat chamber 15. In the preheat chamber, the workpieces are heated under a high order of vacuum to temperatures ranging between 800 and l,000 Fahrenheit and then are shifted into a high heat chamber 16 and are heated up to a temperature as high as 3,000 Fahrenheit, the beating again occurring under a high order of vacuum. Finally, the workpieces are shifted into a cooling chamber 17, are quenched by a cooling gas and are loaded onto a transfer cart 19 at the outboard end of the cooling chamber. The different operations may take place continuously with one batch of workpieces being located in the preheat chamber while another batch is in the high heat chamber and still another in the cooling chamber.

The various chambers I4, 15, 16 and 17 are defined within substantially identical gastight loading, preheat, high heat and cooling vessels 24, 25, 26 and 27 (FIG. 1), respectively, formed with a generally circular cross section and disposed in spaced end-to-end relation. The preheat and high heat chambers 15 and 16 are located within internal walled enclosures 29 and 30 (FIG. 5) of refractory material disposed within the preheat and high heat vessels 25 and 26 and spaced from the walls thereof. The enclosures house heating elements (not shown) and are formed with top, side and end walls, the cars 11 coacting with the side and end walls to close the bottoms of the heat chambers when the cars are shifted into the chambers. A fan 31 (FIG. I) is mounted on the cooling vessel 27 and disposed within the cooling chamber 17 to circulate quenching gas past the workpieces.

To permit passage of the workpieces l0 and the cars 11 between the different chambers 14 to 17, the inboard ends of the loading and cooling vessels 24 and 27 are formed with openings or entryways 33 (FIG. 5), only the entryway in the loading vessel being visible. In addition, aligned entryways 34 are formed in each end of the internal enclosures 29 and 30 in the preheat and high heat vessels 25 and 26. Thus, the workpieces may be shifted on the cars through the various entryways and transferred into and out of the chambers.

In order to enable the purging of the loading chamber 14 with a nonoxidizing gas, the drawing of a vacuum in the preheat and high heat chambers 15 and 16, and the introduction of a cooling gas into the cooling chamber I7, the chambers must be sealed from one another to isolate the atmosphere in each chamber from that in the other chambers. This is accomplished through the use of sealing doors 35 (FIG. 5) which are adapted to be moved to closed positions to establish gastight seals between the chambers. In addition, heat shielding doors 36 are used to selectively close the entryways 34 in the internal enclosures 29 and 30 and to block the escape of heat from the heat chambers I5 and 16 during treating of the workpieces 10, According to the primary aspect of the present invention, the various doors 35 and 36, together with mechanism for moving the doors between open and closed positions, are incorporated within standardized modular units 40 to 44 which may be positioned at or between the ends of the different vessels 24 to 27 to close and/or interconnect the vessels while sealing the chambers 14 to 17 and/or blocking the escape of heat from the chambers as required by the particular operation being performed in the chambers. With the doors contained within the modules 40 to 44 and with the latter being used to join the vessels, the vessels can be connected to and detached from one another quickly and easily and, moreover, additional vessels may be installed as needed simply by connecting door modules between the additional vessels and the existing vessels. Accordingly, the vessels can be arranged as desired and increased in number when necessary thus providing a versatile and flexible heat treating arrangement.

Two basic types of door modules are used in the illustrated heat treating apparatus, the modules 40 and 44 being end-type modules located at the outboard ends of the loading and cooling vessels 24 and 27 while the modules 41, 42 and 43 are center-type modules located between the vessels 24 and 25,

25 and 26, and 26 and 27, respectively. The module 42 is representative of the center-type modules and will be described in detail with the reference numerals used to indicate the parts of the center module 42 also being applied to the center modules 41 and 43 and to certain elements of the end modules 40 and 44.

As shown most clearly in FIGS. to 8, the center module 42 comprises a gastight casing of generally rectangular cross section sandwiched between the vessels 25 and 26 and formed by a top wall 45, sidewalls 46, end walls 47 and 49 and a bottom wall 50. Adjacent the upper portions of the vessels, the sidewalls 46 are formed with inwardly offset portions 51 (FIG. 6) which are connected at their lower ends to the bottom wall, the latter being curved generally in accordance with the curvature of the vessels. Attached rigidly to the end wall 47 and the bottom wall is a wall formed by a circular ring or bulkhead 53 (FIGS. 5 to 8) which faces the end of the vessel 25 and which is formed with a workpiece-admitting opening 54 aligned with the entryway 34 in the internal enclosure 29. The bulkhead 53 is disposed face-to-face with an annular flange 55 encircling the end of the vessel 25 and is detachably connected to the flange by threaded bolts 56 (FIG. 5) which extend through holes 57 (FIG. 8) formed through sets angularly spaced and angularly aligned ears 59 projecting radially from the bulkhead and the flange. A sealing gasket (not shown) extends around and between the bulkhead and the flange to establish a gastight seal between the two.

Rigidly attached to the end wall 49 and the bottom wall 50 of the module 42 is an annular ring 60 FIGS. 5 and 6) which mates face-to-face with an annular flange 55 on the end ofthe high heat vessel 26, the ring and the flange also being sealed to one another and being detachably connected by bolts 56 extending through apertures ears 59 projecting radially from the ring and the flange. An opening 6] (FIG. 5) is formed through the ring 60 and is aligned with the entryway 34 in the internal enclosure 30 to permit passage of the workpieces from the preheat chamber to the high heat chamber 16.

As pointed out above, the sealing and heat shielding doors 35 and 36 advantageously are contained within and form a part of the door modules. In the case of the center module 42, one sealing door and two heat doors are uniquely mounted between the end walls 47 and 49 to seal the opening 54 and to block the escape of'heat through the entryways 34 in the opposing ends of the enclosures 29 and 30. Herein, the heat doors are made of relatively heavy refractory material and each is adapted to be moved to closed position shielding one of the entryways 34. As shown in FIG. 5, each heat door 36 is formed with a main closure section 63 sufficiently large to abut the end of the enclosure and with an inset section 64 sized to fit within the entryway 34. The sealing door 35 is made of relatively lightweight material such as aluminum and, in this instance, is attached to the main section 63 of the heat door for closing the entryway in the enclosure 29. To advantage, the sealing door, when in a closed position as shown in FIG. 5, directly engages the inner face of the bulkhead 53 of the module 42 and seals against the bulkhead to seal the opening 54 and isolate the atmosphere in the preheat chamber 15 from that in the module and the high heat chamber 16. Thus, the sealing surface for the sealing door is provided by the bulkhead within the module itself rather than by a wall of the vessel 25. A sealing gasket (not shown) is attached to the sealing door to insure the establishment ofa gastight seal between the door and the bulkhead.

Advantageously, the sealing door 35 and the two heat doors 36 within the module 42 are mounted to move first vertically to closed positions extending across the respective opening 54 and entryways 34 and then to move laterally to positions in which the sealing door engages and seals against the bulkhead 53 and in which the heat doors abut and engage the enclosures 29 and 30. For these purposes, the doors are mounted on a carriage in the form of a yoke 65 (FIGS. 5 to 7) which is guided for up and down movement in the module. The doors move downwardly with the yoke to their closed positions and,

as the yoke approaches the end of its downward travel, the doors are shifted laterally toward the adjacent entryways 34. As the yoke is moved upwardly, the doors first are moved laterally away from the entryways and then move upwardly with the yoke to open positions above the entryways and the opening 54.

More particularly, the yoke 65 comprises a transversely extending crosshead 66 (FIGS. 5 to 7) to which are connected depending side members 67. The latter carry vertically spaced rollers 69 which ride in center tracks 70 fastened to the offset portions 51 of the sidewalls 46 thereby to guide the yoke for up and down movement. Vertical shifting of the yoke is effected by two hydraulic actuators 71 (FIG. 6) mounted along the outer sides of the offset portions 51 of the sidewalls and having rods 73 projecting into the module and connected to opposite ends of the crosshead 66. The actuators project through and are sealed to horizontal walls 74 (FIG. 6) connecting the sidewalls 46 with the offset wall portions 51, and thus the module 42 is maintained in a gastight condition. As the rods are extended and retracted, the yoke is raised and lowered.

The sealing door 35 and the two heat doors 36 are connected pivotally to the yoke 65 by sets of upper and lower parallel links 75 (FIG. 5) attached pivotally to and extending in opposite directions from the yoke. As shown most clearly in FIG. 5, the links of one set are connected pivotally to the sealing door 35 while the links of the other set are connected pivotally to the heat door 36 for the enclosure 30. Rollers 76 are carried by the ends of the links adjacent the doors and ride within generally upright side tracks 77 fastened to the offset portions 51 of the sidewalls 46 along opposite sides of the center tracks 70. At their lower end portions, the side tracks are curved downwardly and away from the yoke as indicated at 79 in FIG. 5.

As the yoke 65 is shifted downwardly, the upright portions of the side tracks 77 guide the sealing door 35 and the heat doors 36 for downward movement in a generally vertical path until the doors reach positions aligned with and extending across the opening 54 and the entryways 34. Thereafter, the rollers 76 ride into the curved portions 79 ofthe side tracks to cause the links 75 to extend laterally away from the yoke and thereby shift the doors laterally or broadwise. The sealing door 35 thus is pressed laterally into tight-sealing engagement with the bulkhead 53 while the main section 63 of the associated heat door 36 is abutted against the enclosure 29 to block the escape of the heat from the preheat chamber 15. Similarly, the main section of the other heat door 36 is abutted against the enclosure 30 to prevent heat from escaping from the high heat chamber 16. The links 75 hold the sealing door tightly against the bulkhead 53 and thus a tight seal may be maintained even when the pressure in the preheat chamber 15 is greater than that within the module 42. When the yoke is raised, the rollers 76 first ride in the curved portions 79 of the side tracks 77 to cause the doors to shift laterally away from the enclosures 29 and 30 and then move into the upright portions of the tracks to cause vertical lifting of the doors to their open positions.

From the foregoing, it will be apparent that the door module 42 is self-contained in that the sealing door 35 and the two heat doors 36 are built into the module rather than being parts of the vessels 25 and 26 themselves. The vessels thus may be interconnected and the chambers I5 and I6 appropriately closed simply by placing a module between the vessels and by connecting the bulkhead 53 and the ring 60 to the flanges 55 by the bolts 56. It will be seen that the doors and the tracks 70 and 77 are arranged symmetrically relative to the vertically extending centerline of the module such that the closure faces of the heat doors 36 are spaced equidistantly from the centerline. Also, the ends of the enclosures 29 and 30 are spaced approximately the same distance from the ends of the vessels 25 and 26 and thus, if desired, the module 42 may be turned endfor-end and connected to the vessels and yet the heat doors still will tightly abut the enclosures and shield the entryways 34.

The center module 41 is identical to the module 42 except that the module 41 contains only one sealing door 35 and one heat door 36 for sealing the opening 54 and closing the entryway 34 in the outboard end of the enclosure 29 (see FIG. 5). An additional sealing door or heat door could be incorporated in the module 41 simply by adding a second set of side tracks 77 and by connecting the additional doors to the yoke 65 by links 75. The module 43 is exactly the same as the module 41 except that the former module is turned end-forend with the bulkhead 53 located adjacent the outboard end of the high heat chamber 16 and with the sealing and heat doors 35 and 36 closing such chamber. If it is desired to connect an additional high heat vessel to the vessel 26, it is necessary only to add another heat door 36 to the module 43 or to replace the module with one equipped with a high heat door. Because the doors and the actuators 71 may be installed and removed as a unit with a module, it is a relatively simple operation to add or replace modules as desired. Various types of vessels thus may be quickly and easily connected to one another in any particular arrangement required for given production demands thus affording an economical but versatile heat treating apparatus.

As shown most clearly in FIGS. 1, 2 and 5, each of the end modules 40 and 44 also comprises a casing formed in part by an inboard end wall 47 with a bulkhead 53 having an opening 54. The bulkhead of the module 40 is connected face-to-face with the outboard flange 55 of the loading vessel 24 while the bulkhead of the module 44 is fastened to the outboard flange 55 of the cooling vessel 27. The end modules 40 and 44 also include outboard end walls 79 (FIG. 5) formed with exposed workpiece openings 80 aligned with the entryways. A sealing door 35 is mounted on a yoke 65 within each end module by parallel links 75 and is adapted to .be moved vertically and then laterally into sealing engagement with the bulkhead by actuators 71 to seal adjacent chamber 14 and 17 from the outside atmosphere. It will be seen from FIGS. 1,2 and 5 that the end modules 40 and 44 are basically similar to the center modules 41, 42 and 43 with the exception that the end modules house only sealing doors 35 and do not include annular rings 60 on the end walls 79.

The holes 57 through all of the various bulkheads 53, flanges 55 and rings 60 are symmetrically spaced and are arranged around circles of constant diameter. Accordingly, any of the modules 40 to 44 can be connected to the ends ofany of the vessels 24 to 27 thus further increasing the flexibility of the overall heat treating arrangement. For example, if the loading vessel 24 were eliminated, the end module 40 could be used directly adjacent the preheat vessel 25 simply by attaching a heat door 36 to the sealing door 35 within the module.

I claim as my invention:

1. In apparatus for heat treating workpieces, the combination of, two walled vessels disposed in spaced end-to-end relation and each including a heating chamber, the opposing ends of said chambers having aligned entryways permitting passage of the workpieces from one chamber to the other, a self-contained door module sandwiched between the opposing ends of said vessels, said door module comprising:

a. a gastight casing extending between said vessels and having spaced walls detachably connected to the ends of the enclosures and each formed with an opening therethrough aligned with said entryways,

b. two heat shielding doors and one gas sealing door housed within and supported by said casing and each mounted for movement between open and closed positions, said heat shielding doors being disposed adjacent opposite ones of said walls and each extending across and closing the entryway ofthe adjacent chamber when in said closed position thereby to block the escape of heat from such chamber, said gas sealing door being disposed between said heat shielding doors and, when in said closed position, extending across one of said openings and being sealed against the adjacent wall with a gastight seal thereby to isolate the atmosphere in one chamber from that in the other chamber, and

c. means within said casing for moving said doors between said open and closed positions.

2. Apparatus as defined in claim 1 in which said heating chambers are defined by internal enclosures within said vessels, the opposing ends of said enclosures being formed with said entryways and being spaced inwardly substantially the same predetermined distance from the opposing ends of the respective vessels, each of said heat shielding doors having a closure face disposed in engagement with the end of the respective enclosure when the door is in its closed position, and the closure faces of the doors being spaced equidistantly but in opposite directions from a centerline extending through said casing in a plane parallel to said walls whereby the casing may be positioned facing in one direction or the opposite direction while still enabling said closure faces to engage said enclosures and close said entryways.

3. Apparatus as defined in claim 2 further including means within said casing mounting said heat shielding doors for movement between said open and closed positions, said lastmentioned means comprising a carriage located between said heat shielding doors and guided for movement in opposite direction in a plane parallel to said walls, and sets of parallel links extending in opposite directions from said carriage with one set of links connected to one of said heat shielding doors and with the other set of links connected to the other heat shielding door.

4. In apparatus for heat treating workpieces, the combination of, two walled vessels disposed in spaced end-to-end relation and each including a work chamber with one of said chambers being a heating chamber, the opposing ends of said chambers having aligned entryways permitting passage of the workpieces between the chambers, a door module sandwiched between the opposing ends of said vessels, said door module comprising:

a. a gastight casing spanning the ends of said vessels and having spaced walls each formed with an opening therethrough aligned with said entryways,

b. a heat shielding door and a gas sealing door housed within and supported by said casing and each mounted for movement between open and closed positions, said heat shielding door being disposed adjacent the wall closest to said heating chamber and extending across and closing the entryway of the heating chamber when in said closed position thereby to block the escape of heat from such chamber, said gas sealing door being disposed between said heat shielding door and the other of said walls and, when in said closed position, extending across one of said openings and being sealed against the adjacent wall with a gastight seal thereby to isolate the atmosphere in one chamber from the atmosphere in the other chamber,

c. an actuating mechanism within said casing for moving said doors between said open and closed positions, and

d. means detachably fastening said walls to the ends of said vessels whereby the casing releasably interconnects said vessels and may be installed between and removed from the vessels as a unit with said doors and said actuating mechanism.

5. Apparatus as defined in claim 4 further including annular flanges joined to and encircling the opposing ends of said vessels, annular rings joined to and encircling the walls of said casing and disposed face-to-face with said flanges, aligned holes formed through said flanges and said rings, and said fastening means comprising bolts extending through said holes to releasably interconnect said vessels and said casing.

6. Apparatus as defined in claim 5 in which said holes in said flanges and said rings are spaced symmetrically relative to one another around the circumference of a circle with all of said circles being ofthe same diameter.

7. ln apparatus for treating workpieces, the combination of, a walled vessel defining a work chamber, an entryway in one end of said chamber to permit passage of the workpieces into or out of the chamber a door module located at one end of said chamber, said door module comprising:

said one wall,

d. an actuating mechanism within said casing for moving said door between said open and closed positions, and

e. means detachably fastening said one wall to the end of said vessel whereby the casing may be installed on and removed from the vessel as a unit with said door, said mounting means and said actuating mechanism. 

1. In apparatus for heat treating workpieces, the combination of, two walled vessels disposed in spaced end-to-end relation and each including a heating chamber, the opposing ends of said chambers having aligned entryways permitting passage of the workpieces from one chamber to the other, a self-contained door module sandwiched between the opposing ends of said vessels, said door module comprising: a. a gastight casing extending between said vessels and having spaced walls detachably connected to the ends of the enclosures and each formed with an opening therethrough aligned with said entryways, b. two heat shielding doors and one gas sealing door housed within and supported by said casing and each mounted for movement between open and closed positions, said heat shielding doors being disposed adjacent opposite ones of said walls and each extending across and closing the entryway of the adjacent chamber when in said closed position thereby to block the escape of heat from such chamber, said gas sealing door being disposed between said heat shielding doors and, when in said closed position, extending across one of said openings and being sealed against the adjacent wall with a gastight seal thereby to isolate the atmosphere in one chamber from that in the other chamber, and c. means within said casing for moving said doors between said open and closed positions.
 2. Apparatus as defined in claim 1 in which said heating chambers are defined by internal enclosures within said vessels, the opposing ends of said enclosures being formed with said entryways and being spaced inwardly substantially the same predetermined distance from the opposing ends of the respective vessels, each of said heat shielding doors having a closure face disposed in engagement with the end of the respective enclosure when the door is in its closed position, and the closure faces of the doors being spaced equidistantly but in opposite directions from a centerline extending through said casing in a plane parallel to said walls whereby the casing may be positioned facing in one direction or the opposite direction while still enabling said closure faces to engage said enclosures and close said entryways.
 3. Apparatus as defined in claim 2 further including means within said casing mounting said heat shielding doors for movement between said open and closed positions, said last-mentioned means comprising a carriage located between said heat shielding doors and guided for movement in opposite direction in a plane parallel to said walls, and sets of parallel links extending in opposite directions from said carriage with one set of links connected to one of said heat shielding doors and with the other set of links connected to the other heat shielding door.
 4. In apparatus for heat treating workpieces, the combination of, two walled vessels disposed in spaced end-to-end relation and each including a work chamber with one of said chambers being a heating chamber, the opposing ends of said chambers having aligned entryways permitting passage of the workpieces between the chambers, a door module sandwiched between the opposing ends of said vessels, said door module comprising: a. a gastight casing spanning the ends of said vessels and having spaced walls each formed with an opening therethrough aligned with said entryways, b. a heat shielding door and a gas sealing door housed within and supported by said casing and each mounTed for movement between open and closed positions, said heat shielding door being disposed adjacent the wall closest to said heating chamber and extending across and closing the entryway of the heating chamber when in said closed position thereby to block the escape of heat from such chamber, said gas sealing door being disposed between said heat shielding door and the other of said walls and, when in said closed position, extending across one of said openings and being sealed against the adjacent wall with a gastight seal thereby to isolate the atmosphere in one chamber from the atmosphere in the other chamber, c. an actuating mechanism within said casing for moving said doors between said open and closed positions, and d. means detachably fastening said walls to the ends of said vessels whereby the casing releasably interconnects said vessels and may be installed between and removed from the vessels as a unit with said doors and said actuating mechanism.
 5. Apparatus as defined in claim 4 further including annular flanges joined to and encircling the opposing ends of said vessels, annular rings joined to and encircling the walls of said casing and disposed face-to-face with said flanges, aligned holes formed through said flanges and said rings, and said fastening means comprising bolts extending through said holes to releasably interconnect said vessels and said casing.
 6. Apparatus as defined in claim 5 in which said holes in said flanges and said rings are spaced symmetrically relative to one another around the circumference of a circle with all of said circles being of the same diameter.
 7. In apparatus for treating workpieces, the combination of, a walled vessel defining a work chamber, an entryway in one end of said chamber to permit passage of the workpieces into or out of the chamber a door module located at one end of said chamber, said door module comprising: a. a casing having spaced walls each formed with an opening therethrough aligned with said entryway, b. a door housed within and supported by said casing adjacent one of said walls c. means within said casing mounting said door for movement from an open position to a closed position first along a linear path across the opening in said one wall and then laterally of said path and toward said opening and said one wall, d. an actuating mechanism within said casing for moving said door between said open and closed positions, and e. means detachably fastening said one wall to the end of said vessel whereby the casing may be installed on and removed from the vessel as a unit with said door, said mounting means and said actuating mechanism. 